Photo booth black screen

When I start Photo Booth, my MacBook Pro (about three years old) just goes to a black screen. The webcam light is still on, and I can hear the fan running, but I can't shut the program down or do anything other than a forced shut down.

Test your camera again by starting the Facetime.app which you should have on your MBP. If the camera turns on and you see yourself, then it's working OK and the problem could be with the Photo Booth.app. Let us know and we can go from there.